The present disclosure relates to systems and methods for applying a coating layer of a liquid functional material on an imaging member surface.
Electrostatographic and xerographic reproductions may be initiated by depositing a uniform charge on an imaging member (i.e., photoreceptor), followed by exposing the imaging member to a light image of an original document. Exposing the charged imaging member to a light image causes discharge in areas corresponding to non-image areas of the original document while the charge is maintained on image areas, creating an electrostatic latent image of the original document on the imaging member. The latent image is subsequently developed into a visible image by depositing a charged developing material (i.e., toner) onto the photoconductive surface layer, such that the developing material is attracted to the charged image areas on the imaging member. Thereafter, the developing material is transferred from the imaging member to a copy sheet or some other image support substrate to which the image may be permanently affixed for producing a reproduction of the original document. In a final step in the process, the imaging member is cleaned to remove any residual developing material therefrom, in preparation for subsequent imaging cycles.
The described electrophotographic copying process is well known and is commonly used for light lens copying of an original document. Analogous processes also exist in other electrophotographic printing applications such as, for example, digital laser printing and reproduction where charge is deposited on a charge retentive surface in response to electronically generated or stored images.
To charge the surface of a photoreceptor (P/R), a contact type charging device has been used, such as disclosed in U.S. Pat. Nos. 4,387,980 and 7,580,655, which are incorporated herein by reference in their entireties. The contact type charging device, also termed “bias charge roll” (BCR), includes a conductive member which is supplied a voltage from a power source with a D.C. voltage superimposed with an A.C. voltage of no less than twice the level of the D.C. voltage. The charging device contacts the image bearing member (photoreceptor) surface, which is a member to be charged.
Electrophotographic photoreceptors can be provided in a number of forms. For example, the photoreceptors can be a homogeneous layer of a single material, such as vitreous selenium, or it can be a composite layer containing a photoconductive layer and another material. In addition, the photoreceptor can be layered. Multilayered photoreceptors or imaging members have at least two layers, and may include a substrate, a conductive layer, an optional undercoat layer (sometimes referred to as a “charge blocking layer” or “hole blocking layer”), an optional adhesive layer, a photogenerating layer (sometimes referred to as a “charge generation layer,” “charge generating layer,” or “charge generator layer”), a charge transport layer, and an optional overcoating layer in either a flexible belt form or a rigid drum configuration. In the multilayer configuration, the active layers of the photoreceptor are the charge generation layer (CGL) and the charge transport layer (CTL). Enhancement of charge transport across these layers provides better photoreceptor performance. Multilayered flexible photoreceptor members may include an anti-curl layer on the backside of the substrate, opposite to the side of the electrically active layers, to render the desired photoreceptor flatness.
In recent years, organic photoreceptors have been widely used for electrographic purposes. This is because organic photoreceptors are easy to prepare at low cost and have the advantages of mechanical flexibility, easy disposability and environmental sustainability. However, the microcorona generated during repetitive charging damages the organic photoconductor, resulting in a rapid wear of the imaging surface and shortening the life of the photoreceptor.
To further increase the service life of the photoreceptor, use of overcoat layers has also been implemented to protect photoreceptors and improve performance, such as wear resistance. However, these low wear overcoats are associated with poor image quality in a humid environment as the wear rates decrease to a certain level. In addition, high friction associated with low wear overcoats in the humidity environment also causes severe issues with BCR charging systems, such as motor failure due to high friction/torque and blade damage. As well, toner or additive particles remaining on the photoreceptor after transferring could not be effectively cleaned by the cleaning blade. As a result, use of a low wear overcoat with BCR charging systems is still a challenge, and there is a need to find ways to increase the life of the photoreceptor with excellent image quality and charging performance.
An applicator to apply functional material (such as paraffin oil) to the surface of the photoreceptor was disclosed in U.S. patent application Ser. Nos. 13/279,981 and 13/326,414, which are hereby incorporated in their entireties by reference herein. The applied thin layer of functional material addresses image deletion, alleviates chattering of the cleaning blade, and reduces toner/additive contamination on the BCR. However, as a roll-type design, it is difficult to control the contact force of the roller surface of the applicator against the surface of the photoreceptor or the BCR along the entire length during rotation, which affects the rate of diffusion of oil from the delivery roller and results in an uneven distribution of oil, particularly at the two ends of the photoreceptor or BCR surface. As a result, after long term prints, toner density across a page becomes uneven, thus the edges of the images sometimes become darker than the middle due to an excess amount of delivered oil. This can further cause the delivery roller to become contaminated with toner and additives over time due to inefficient cleaning of the surface of the photoreceptor (P/R) by the cleaning blade. Toner particles are eventually transferred to and contaminate the surface of the BCR.
In U.S. patent application Ser. No. 13/437,472, a blade applicator to apply an ultrathin layer of liquid phase functional materials on the surface of a P/R or a surface of a BCR is described. The blade applicator is in contact with the P/R surface or the BCR surface in a trailing configuration. However, the friction between the applicator and the surface of the P/R or the surface of the BCR can cause the contact edge on the blade to wear and cause non-uniform diffusion of the functional material on the surface of the P/R or the surface of the BCR. In addition, long term wear of the contact edge of the blade can result in contamination of toner or additives which can lever the blade edge away from surface of the P/R or the surface of the BCR, creating areas on the surface of the P/R or the surface of the BCR where no functional material is applied. This can cause damage of cleaning blade and image failure.
It would be desirable to develop contactless systems and methods for applying functional materials to an imaging member surface which permit accurate control of the amount of the functional material, without degrading image quality.